1. Field of the Invention
The present invention relates to a surface light source control device usable for a liquid crystal display device, and more particularly relates to such a surface light source control device for making a power supply voltage, which is applied to a plurality of arrays of light emitting diodes composing a plane light source section, low in power consumption on the plurality of light emitting diode arrays.
2. Description of the Related Art
Some conventional liquid crystal display devices adopt plane light source sections using light emitting diodes as backlights. Each of these light source sections has a light emitting diode (LED) light source equipped with a plurality of diode arrays with a plurality of LEDs serially arrayed thereon. A power supply voltage with a fixed value is applied to one common terminal of the plurality of LED arrays. Adjusting resistors are connected between the other common terminal and the ground of the plurality of LED arrays, respectively. Then, the display device adjusts adjustment resistors of each LED array so as to pass currents with the same value thereto.
This is because the currents flowing into each LED array vary in accordance with differences of each property of the LEDs. That is, if there are variations in current value among the LED arrays, brightness of each array varies. Moreover, there is a problem in that an excess current flows into each LED array to cause reductions in service life of each LED. Therefore, the display device adjusts the adjustment resistors of each array in order to suppress the variations in the brightness.
As to a technique similar to the above-mentioned technique, a technique using a constant current circuit so as to control a current flowing into the LED is disclosed (See Jpn. Pat. Appln. Publication No. 11-298044). This current circuit controls a current to suppress the variations in brightness in accordance with variations of a surrounding temperature, based on the temperature fluctuation.
However, the foregoing conventional liquid crystal display device needs adjustment operations for the adjustment resistors and requires much time and cost for assembly operations. Since power supply voltages applied to each LED array are usually selected as ones with maximum values which can be applied to each LED array, it is impossible to reduce the power consumption of the diode arrays.